[Issue 24301] New: [REG 2.100] Misleading error message when passing non-copyable struct by value in @safe code

[d-bugmail at puremagic.com]

https://issues.dlang.org/show_bug.cgi?id=24301

          Issue ID: 24301
           Summary: [REG 2.100] Misleading error message when passing
                    non-copyable struct by value in @safe code
           Product: D
           Version: D2
          Hardware: All
                OS: All
            Status: NEW
          Severity: regression
          Priority: P1
         Component: dmd
          Assignee: nobody at puremagic.com
          Reporter: snarwin+bugzilla at gmail.com

As of DMD 2.106.0, when attempting to compile the following program:

---
struct S
{
        @disable this(ref S);
}

@safe void fun(S) {}

@safe void main()
{
        S s;
        fun(s);
}
---

...the following error message is produced:

---
bug.d(11): Error: function `bug.fun(S __param_0)` is not callable using
argument types `(S)`
bug.d(11):        `ref S(ref S)` copy constructor cannot be called from a
`@safe` context
---

This message is misleading. The reason the copy constructor cannot be called is
that it is marked with @disable, and has nothing to do with @safe.

According to run.dlang.io, this misleading message was introduced between DMD
2.099.1 
and 2.100.2:

2.086.1 to 2.099.1: Failure with output:
-----
onlineapp.d(11): Error: function `onlineapp.fun(S _param_0)` is not callable
using argument types `(S)`
onlineapp.d(11):        `struct S` does not define a copy constructor for `S`
to `S` copies
-----

2.100.2 to 2.103.1: Failure with output:
-----
onlineapp.d(11): Error: function `onlineapp.fun(S _param_0)` is not callable
using argument types `(S)`
onlineapp.d(11):        `ref S(ref S)` copy constructor cannot be called from a
`@safe` context
-----

--